Large turbomachinery rotors have to be rotated during cool down at least at a low speed to assure a uniform cool down (rotor turning/barring operation). The required rotation of the rotor is actuated by special devices (rotor barring or rotor turning devices).
During cool down large temperature deviations are present in the flow channel in circumferential direction by natural convection. If this circumferential temperature deviation is transferred to the rotor, the rotor will bend due to the uneven thermal expansion. Bending of the rotor may lead to contact of the rotor with the stator resulting in a blockage of the rotation. A blocked rotor leads to the unavailability of the turbomachine for operation. Contact between the rotor and stator leads to deterioration of the part condition by rubbing.
Document U.S. Pat. No. 4,905,810 A discloses an apparatus and method for periodic rotation of the rotor assembly of a turbogenerator during the time that it is not rotated in its normal manner for generating power, in which a continuously operating motor is periodically connected through an electrically controllable, torque-speed, clutch mechanism and a gear train to a gear mounted on the rotor shaft so as to rotate the shaft by 180° at a slow speed. The position of the rotor is measured by electrically counting the teeth of the gear on the rotor shaft, and the count of teeth is compared with a preset number in a counter which after the count set in the counter is reached, disconnects the motor from the rotor gear and sets a brake. A settable timer periodically releases the brake and connects the motor to the rotor gear. The apparatus can include a recorder for recording rotation of the shaft and an alarm for indicating failure of rotation of the rotor when the timer provides a start signal.
Document U.S. Pat. No. 4,267,740 A discloses an apparatus for rotating a shaft of a turbine. This apparatus includes a ratchet wheel which is connected to the shaft, and a pawl which engages the teeth of the ratchet wheel. The teeth of the ratchet wheel have bearing surfaces with convex curvatures, while the pawl has a contact surface which also has a convex curvature.
Document EP 0 266 581 A1 discloses an installation for turning the shaft of a turbo set by means of a hydraulic geared motor with interconnection of an overrunning clutch, the shaft being mounted in several hydrodynamic bearings, which preferably also have oil inlets of a shaft-lifting system, characterised in that hydraulic geared motor and overrunning clutch are secured, in alignment with the shaft, to the front wall of the foremost bearing of the shaft, in that, furthermore, the overrunning clutch is mounted by means of rolling bearings and the foremost bearing of the shaft has an additional hydrostatic mounting for the purpose of centering with respect to the overrunning clutch.
Document GB 564,519 A discloses a barring mechanism for the rotors of various kinds of machines and engines, comprising fluid pressure actuated pistons and ratchet gears driven thereby.
However, the existing rotor barring actuators rotate the turbomachine rotor with a constant circumferential speed and can not react to a bending of a rotor which starts to develop.